The invention relates to a method for operating a multiphase electric machine which has a rotor and a rotary encoder, which is connected to the rotor, wherein an actual rotation angle of the rotor is determined from a measured rotation angle determined by the rotary encoder and a rotation angle offset. The invention also relates to a multiphase electric machine.
Many applications require to control the (multiple) phases of the electric machine—which for example is constructed as synchronous machine—in dependence on the currently present actual rotation angle of the rotor. Correspondingly it is required to determine the actual rotation angle with high accuracy. For this purpose the rotary encoder is provided. However, because it is oftentimes not possible to first bring the rotor into a exactly defined position and to subsequently connect the rotary encoder with the rotor, the rotary encoder can only provide the measured rotation angle, which however depending on the rotation angle of the rotor during mounting of the rotary encoder of the rotor deviates from the actual rotation angle by the rotation angle offset.
This rotation angle offset must therefore be determined in order to determine the actually present actual rotation angle of the rotor. One possibility is for example to measure the phase voltages that are present in the phases of the electric machine, because the phase angle of these phase voltages can provide an indication of the actual rotation angle of the rotor. For this purpose it would have to be possible to measure these phase voltages, which, however, oftentimes is not the case. This applies in particular when the electric machine is used for driving a hybrid or electric vehicle. The power electronics used in this case for controlling the individual phases of the electric machine in most cases simply do not offer the possibility to determine the phase voltages. From the state of the art for example the published patent application DE 2011 089 341 A1 is known. This published patent application discloses a method for determining an angle between a stator and a rotor of a externally excited synchronous machine.